Add utility program for emitting P-256 x86-64 table.

No semantic change: the table is the same as before, but now with less
magic.

Change-Id: I351c2446e9765f25b7dfb901c9e98f12099a325c
Reviewed-on: https://boringssl-review.googlesource.com/26744
Reviewed-by: Adam Langley <agl@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

crypto/fipsmodule/ec/make_p256-x86_64-table.go

@@ -0,0 +1,130 @@
+/* Copyright (c) 2018, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+package main
+
+import (
+	"crypto/elliptic"
+	"fmt"
+	"math/big"
+	"os"
+)
+
+const fileHeader = `/* Copyright (c) 2015, Intel Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+// This is the precomputed constant time access table for the code in
+// p256-x86_64.c, for the default generator. The table consists of 37
+// subtables, each subtable contains 64 affine points. The affine points are
+// encoded as eight uint64's, four for the x coordinate and four for the y.
+// Both values are in little-endian order. There are 37 tables because a
+// signed, 6-bit wNAF form of the scalar is used and ceil(256/(6 + 1)) = 37.
+// Within each table there are 64 values because the 6-bit wNAF value can take
+// 64 values, ignoring the sign bit, which is implemented by performing a
+// negation of the affine point when required. We would like to align it to 2MB
+// in order to increase the chances of using a large page but that appears to
+// lead to invalid ELF files being produced.
+
+// This file is generated by make_p256-x86_64-table.go.
+
+static const alignas(4096) BN_ULONG
+    ecp_nistz256_precomputed[37][64 * sizeof(P256_POINT_AFFINE) /
+                                 sizeof(BN_ULONG)] = {
+`
+
+func main() {
+	os.Stdout.WriteString(fileHeader)
+
+	scalar, tmp := new(big.Int), new(big.Int)
+	p256 := elliptic.P256()
+	p := p256.Params().P
+
+	// The wNAF windows are 7 bits wide, so advance across the 256-bit scalar
+	// space in 7-bit increments.
+	for shift := uint(0); shift < 256; shift += 7 {
+		// For each window, encode 64 multiples of the base point.
+		for multiple := 1; multiple <= 64; multiple++ {
+			scalar.SetInt64(int64(multiple))
+			scalar.Lsh(scalar, shift)
+
+			x, y := p256.ScalarBaseMult(scalar.Bytes())
+
+			toMontgomery(x, p)
+			toMontgomery(y, p)
+
+			if multiple == 1 {
+				os.Stdout.WriteString("        {")
+			} else {
+				os.Stdout.WriteString("         ")
+			}
+			printNum(x, tmp)
+
+			os.Stdout.WriteString(",\n         ")
+			printNum(y, tmp)
+
+			if multiple == 64 {
+				os.Stdout.WriteString("}")
+			} else {
+				os.Stdout.WriteString(",\n")
+			}
+		}
+
+		if shift + 7 < 256 {
+			os.Stdout.WriteString(",\n")
+		} else {
+			os.Stdout.WriteString("};\n")
+		}
+	}
+}
+
+var mask, R *big.Int
+
+func init() {
+	mask = new(big.Int).SetUint64(0xffffffffffffffff)
+	R = new(big.Int).SetInt64(1)
+	R.Lsh(R, 256)
+}
+
+func printNum(n, tmp *big.Int) {
+	for i := 0; i < 4; i++ {
+		tmp.And(n, mask)
+		limb := tmp.Uint64()
+		fmt.Printf("TOBN(0x%08x, 0x%08x)", uint32(limb>>32), uint32(limb))
+		n.Rsh(n, 64)
+
+		switch i {
+		case 0, 2:
+			os.Stdout.WriteString(", ")
+		case 1:
+			os.Stdout.WriteString(",\n         ")
+		}
+	}
+}
+
+// toMontgomery sets n to be n×R mod p
+func toMontgomery(n, p *big.Int) {
+	n.Mul(n, R)
+	n.Mod(n, p)
+}